If you grew up on Chicago's South Side in the 1960s, you were close to the AACM whether you wanted to be or not. Fred Hopkins came up in that world, studying classical bass alongside gigging on the scene that produced Henry Threadgill, Muhal Richard Abrams, and a whole generation of players who didn't see why jazz had to stay inside its own fences. By the time Hopkins joined Threadgill and drummer Steve McCall in the group that became Air, he already had the technique to do anything and the ears to know when not to.

Air is the reason most people know Hopkins's name, and for good reason. On records like Air Lore (1979), where the trio reworked Scott Joplin and Jelly Roll Morton tunes through a completely free-jazz lens, Hopkins is the glue holding the whole experiment together. Threadgill could go anywhere on reeds and flute, McCall could scatter rhythm in a dozen directions, and Hopkins was the one who made sure it all still felt like music and not just noise for its own sake. He had a huge, woody sound, and he used the bow almost as much as he plucked, getting a singing, almost vocal quality out of the instrument that few of his peers bothered to chase.

Outside Air, Hopkins became one of the most in-demand bassists in the loft jazz and downtown scenes, which tells you something — these were not easy gigs for a timekeeper who just wanted to lay down changes. He worked with David Murray on albums like Ming (1980), with Arthur Blythe, with Lester Bowie, moving between free improvisation and tightly arranged post-bop without ever sounding like a tourist in either camp. People talk about versatility in jazz bassists like it's a given, but Hopkins's range was unusual even by the standards of his generation.

He never became a household name, and that's partly the nature of the instrument — nobody puts the bassist's face on the album cover — and partly because Hopkins seemed content being the musician other musicians wanted in the room. He died in 1999, still working, still showing up for sessions that needed someone who could play free and play straight in the same afternoon. If you want to understand what made Chicago's avant-garde scene function as music rather than chaos, start with his bass lines underneath it.